Rattle

I have an rattling noise when I shut the car off, but dont hear it when clutch is depressed (throwout bearing??). And can hear it when I start it in the mornings at idle, but for a brief moment. When i drive off, or rev engine it goes away and doesnt return. Is it the dual-flywheels??Clutch (throwout bearing)?? Help please. BTW I reported it during my manufacture warranty. . . they couldnt find the problem, now in CPO (66,000 miles), and pretty sure they'll find the problem.